Cerebellum and Basal Ganglia Physiology

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Describe the basic circuit common to all parts of the cerebellum. Compare the functions of the mossy and climbing fiber input

Basic circuit.png
  • the basic circuit has three parts
    1. direct pathway - input projects directly to motor systems via the deep cerebellar nuclei
    2. indirect side loop - mossy fiber input to granular cells
      • used to correct reflex responses
    3. climbing fiber input - goes to purkinje cells
      • helps in learning processes
      • used in error detection

Basically, the basic circuit aims to take a sensory input and turn into into a motor command. Everything else just consists of manipulations of this system -- corrections, attenuations, and exaggerations.

Draw a diagram indicating the three functional divisions of the cerebellum and draw the major input-output connections of each region. List the main functions of each division

Vestibulocerebellum

  • Input - from vestibular organs
  • Output - to legs, trunk and eye muscles
  • Functions - tunes balance (stance and gait) and VOR (Vestibulo-ocular Reflex)

Spinocerebellum

  • Input - spinal cord (somatosensory & muscle afferents), visual and auditory
  • Output - to spinal cord (via red and reticular nerves; motor cortex)
  • Functions - tunes motor execution by adjusting muscle tone and movements

Cerebro cerebellum

  • Input - from cerebral cortex
  • Output - to motor and premotor cerbral cortex
  • Functions - initiation of skilled movements

Describe the possible role of climbing fibre and mossy fibre input in motor learning. Give two examples of cerebellar learning

Roles

  • Mossy fibre input - Provides an ongoing correction of the VOR, say
  • Climbing fibre - When it detects problems, such as a slip of the field of view, it semi-permanently alters synaptic pathways to to adjust.

Examples

  1. Darts thrown at a board with displacement prism
  2. Trying to balance on a board on a ball

Describe the motor circuit of the basal ganglia. Describe its role in movement generation

  • loop begins and ends in the cerebral cortex
  • path: cerebral cortex projects to striatum then to globus pallidus and substantia nigra, then to the thalamus, and finally back to supplementary motor and premotor cortices (the two regions involved in motor planning and selecting movements.
  • the overall function is to select some movements while suppressing others.
  • Movement generation
    • ????


Contrast the role of the basal ganglia in Parkinson and Huntington's disease

Parkinson's

  • Difficulty in initiating movements
    • There is too much inhibition of thalamus due to dopamine insufficiency
    • Treatment is L-Dopa, but too much L-Dopa causes spontaneous movement due to too little inhibition

Huntington's

  • Too little inhibition of the Thalamus, so spontaneous movement is initiated

Compare the motor deficits in cerebellar diseases and those of the basal ganglia (Parkinson's)

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